Known boiler systems include a boiler connected to an external control such as a thermostat or a building management system. The external control typically senses boiler temperature, controls boiler setpoint, performs outdoor reset functions and controls the boiler firing cycle.
In multiple boiler systems, each boiler is connected to a single centralized external control from which all boiler operations are performed. The centralized control typically performs the above-listed functions for each individual boiler as well as sequencing or staging the firing of all boilers to control heating throughout a structure. To accomplish this, each boiler is separately connected to the external control via wiring that is run within the structure to be heated. Moreover, boiler wiring is generally run through conduits to protect the wiring and ensure the reliability of the system.
As will be appreciated, multiple boiler systems can be costly to purchase and install as they require significant wiring from the external control to each individual boiler. In one known system, for example, control cables between a boiler control module and individual boilers consist of extended runs of 3-wire circuits. As stated, such wiring is typically protected with a conduit of plastic or like material, which requires installation.
Moreover, the addition of a boiler in known multiple boiler systems requires supplemental wiring to connect the new boiler to the external control. The subtraction of a boiler from such systems requires removal of control wiring which can also be costly. Further, the addition or subtraction of a boiler may also necessitate manually resetting or adjusting the external control, such as a building management system, to account for a changed number of total boilers. It is also possible that the existing external control may not have the capacity for an additional boiler and may require modification or replacement.
Additionally, if a boiler is not functioning properly or requires routine maintenance, it must be brought offline. In known systems, bringing an individual boiler offline can necessitate shutting the entire system down creating a no heat situation within a structure. Such system-wide shutdowns can be undesirable particularly when the outside air temperature is low. Further, if a boiler is not functioning properly manual adjustment of the external control may be necessary to adjust the firing of the other boilers to compensate for the faulted unit. Manual adjustment may also be required to bring a previously failed boiler back online if the fault resolves itself. As will be appreciated, manual adjustment of an external control can be time consuming and can result in periods of insufficient heat until adjustment is complete.
Furthermore, in known multiple boiler systems, individual boilers are typically fired in a first on/first off or first on/last off methodology. Neither of these approaches, however, directly assesses which individual boiler has the least runtime. As will be apparent, it is generally desirable to evenly distribute runtime among all boilers in a multiple boiler system. If runtimes are not uniformly distributed, premature maintenance of the more frequently used boilers may be necessary.
Finally, known external controls typically consist of numerous components. These components can include, for example, an outdoor air temperature sensor, an outdoor reset control, a control module and a terminal board. As will be appreciated, it is advantageous to reduce the number of required components to diminish the possibility of failure and reduce purchase and installation costs.
With the forgoing problems and concerns in mind, it is the general object of the present invention to provide a modular boiler control which overcomes the above-described drawbacks and which eliminates the need for a separate connection between individual boilers and a centralized external control in a multiple boiler system.